A technique for forming a composite image on a photosensitive surface based upon a series of elemental images formed successively on the screen of a cathode ray tube is particularly useful in the medical domain to regroup onto a single film several distinct views relating to a single examination. This is the case, for example, with images obtained electronically by scanners, nuclear medicine apparatus or ultrasound apparatus. The difficulty lies in preserving high image quality (when it is desired, for example, to locate tumors of small dimensions) without any reduction in quality due to transposition.
This transposition or transfer of the electronic image onto a reduced zone of a photosensitive surface such as a film, has been achieved by apparatus known as "multi-imagers" where the image of the cathode tube is projected onto a film by an optical system. The composition of different views on the film has been obtained by relative translational movements between the tube, the film and the optical system, in a manner so as to place the screen image projected on the film onto the zone of the film which must be imprinted.
In such systems, when it is desired to produce compositions having variable formats (particularly to vary the total number of views registered on the film), this can be achieved either by changing the screen-optical-film distances to modify the reduction or magnification ratio, or by employing several different optical foci selectively placed in the optical trajectory as a function of the desired format.
A first series of disadvantages of such apparatus results from the presence of moving parts. The machining precision must be very high, a factor which considerably increases the costs of manufacture. In effect, the positioning must be performed with a precision down to several tens of microns; furthermore, play can rapidly appear with time, thereby diminishing this precision.
Furthermore, the repeated movements of the various parts cause, particularly for multi-format apparatus, poor reproduction of the results.
In a patent application entitled "Electronic Multi-Imager Device" invented by D. Inbar, filed on Oct. 19, 1983, bearing Ser. No. 543,043, U.S. Pat. No. 4,514,072, and assigned to the assignee of this application a multi-imaging device is disclosed wherein the optical components remain stationary and individual images on a cathode ray tube screen of a video system are positioned electronically. Basically the positioning is accomplished by delaying the image producing data for desired time spans following horizontal and/or vertical sync pulses. Varying the rate of supplying the image data to the video tube varies the size of the image. While the device of that application represents a vast improvement over the mechanically operated optical systems of the prior art multi-imaging devices, the electronic system described is not the only way of obtaining multi-images without there being movement between the components of the optical system.
It is therefore an object of the present invention to provide a process and apparatus for forming multiple electronic images on a photosensitive surface which also substantially overcomes the above-described deficiencies in the prior art and which has no moving parts and allows for the multiplication of the formats while, nevertheless, preserving an unique optical system which avoids the difficulties related to the use of multiple lens.